Breastmilk and blood samples will be obtained from these patients at pre-specified times after they take the clinically indicated medication, and the concentrations in both matrices will be compared to estimate degree of transfer. Estimation of nifurtimox transfer into breastmilk will allow the evaluation of potential degree of exposure of infants breastfed by these women to nifurtimox. This study will help clarify safety of continuing breastfeeding while receiving treatment with nifurtimox for Chagas disease.